Pyrene Functionalized Mechanochromic Elastomer with Switchable White Fluorescence

Abstract

Mechanochromic polymers that change their photophysical properties on activation by mechanical force are now widely studied, which can signal mechanical stress and visualize material damage ahead of structure failure. However, white‐light‐emitting mechanochromic materials are still very rare. Here, a pyrene group is introduced into a mechanochromic elastomer. A blue‐green fluorescence is exhibited in the original elastomer through rational control of the aggregation degree of pyrene groups. During continuous stretching, due to the “closed” form of rhodamine‐based mechanophore changing into “opened” form, a remarkable white fluorescence can be seen in this process (chromaticity coordinate: x = 0.31, y = 0.31). In the processes of stretching and relaxing, an obvious red shift in fluorescence is detected by the naked eye, which is useful to monitor transient stress in polymer materials. The present study provides a new guideline of the molecular structure design for white‐light emitting mechanochromic materials.

Mechanochemical tools for polymer materials

“…Interestingly, the fluorescent color can be tailored by incorporating pyrene in the polymer material. 53 Upon stretching, the combination of green fluorescence from the pyrene excimer, blue fluorescence from monomeric pyrene and red fluorescence from mechanochemicallyactivated rhodamine gives rise to white emission.…”

Mechanochromophore‐Linked Polymeric Materials with Visible Color Changes

“…In a more recent work, Wang et al introduced pyrene groups into the third network of an Rh‐linked P n BA triple‐network. [ 135 ] Zhang and co‐workers employed the same “tri‐arm” Rh and a micellar copolymerization approach to prepare Rh‐linked mechanochromic hydrogels, which was similar to the strategy of synthesizing SP‐linked micelle‐based hydrogels shown in Figure 6B. [ 136 ] In another work, tri‐functionalized Rh was incorporated into a double network hydrogel (Figure 7C).…”

“…[198] White fluorescence, under deformation, has been achieved by incorporating pyrene groups into a Rh-linked PnBA triplenetwork. [135] Prior to stretching, the combination of green fluorescence from the pyrene excimer, blue fluorescence from monodispersed pyrene, and ring-closed Rh provided the elastomer with blue-green fluorescence. Upon deformation, the ring-open Rh isomer exhibited red fluorescence, leading to a white fluorescence as a result of the combination of blue, green, and red.…”

Mechanochromic polymers with a multimodal chromic transition: mechanophore design and transduction mechanism

“…Mixed colour and bimodal transitions were observed in a combination of mechanophores with undifferentiated mechanical properties located in a similar environment, resulting in simultaneous activation under mechanical force. To date, several concepts have been reported for non-discriminatory responses from diverse mechanophores that demonstrate different colours by employing a single mechanochromic molecule, 65 pyrene excimers, 66 or fluorophores attached to rotaxanes.…”